The present invention relates generally to methods and equipment utilized in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a fluid column weight correction using discrete point and fiber optic temperature measurement.
It is known to use a fluid column extending to the surface for measuring pressure in a well. An example of such a pressure measurement system is described in U.S. Pat. No. 5,163,321, the entire disclosure of which is incorporated herein by this reference.
Typically, a tube is inserted into the well from the surface to the depth at which pressure is to be monitored. The tube is then pressurized with a gas (such as helium or hydrogen) or other fluid. The tube is purged, so that it contains only the pressurized gas or other fluid, and the pressure at a proximal end of the tube is measured as an indication of pressure in the well at a distal end of the tube.
Of course, the weight of the fluid in the tube affects the pressure measurement, and so various attempts have been made in the past to correct the pressure measurement to account for the fluid weight. One method is to estimate an average temperature of the fluid, and then use this average temperature to estimate a density of the fluid, and thereby calculate a total weight of the fluid at the distal end of the tube. Another method is to use a distributed temperature sensing system to obtain a more accurate measurement of temperature along the tube, and then use this temperature distribution to estimate the density of the fluid and, thus, its weight.
It will be appreciated by those skilled in the art that these prior methods provide only rough estimates of the effect of the fluid weight on the pressure measurement. In particular, the fluid weight is not accurately determined, since it is based on inaccurate calculations of the fluid density. Therefore, it may be seen that improvements are needed in the art of correcting pressure measurements for fluid column weight.